Recently, there has been a renewal of interest in manganese deposition on the sea bed, particularly that brought about by biological rather than inorganic processes. During the past fifty years various theories have been, put forward concerning the method of manganese deposition, yet the only measurements on the rate of deposition are those of Petterssen, and Buttler and Houtermans on manganese nodules of deep-sea origin. These authors give a rate of the order of 1 mm. in 1,000 years.